The present invention relates to a piston-type compressor used, for example, in vehicle air-conditioners.
FIGS. 9 and 10 show a typical variable displacement compressor. A compressor housing 101 includes a crank chamber 102 and a rotatably supported drive shaft 103. A lug plate 104 is fixed to the drive shaft 103 in the crank chamber 102. A swash plate 105 is coupled to the lug plate 104 through a hinge mechanism 106. The lug plate 104 and the hinge mechanism 106 cause the swash plate 105 to rotate integrally with the drive shaft 103 and to incline relative to the drive shaft 103.
Six cylinder bores 107 are formed in the housing 101 and are arranged about the axis L of the drive shaft 103 at equal intervals. A piston 108 is accommodated in each cylinder bore 107 and is coupled to the swash plate 105 through shoes 109. When an external drive source, such as a vehicle engine, rotates the drive shaft 103, the swash plate is rotated by the lug plate 104 and the hinge mechanism 106. Rotation of the swash plate 105 is converted into reciprocation of the pistons 108 through the shoes 109. The reciprocation of the pistons 108 repeats a cycle of drawing refrigerant gas to the cylinder bores 107, compressing the refrigerant gas, and discharging the refrigerant gas from the cylinder bores 107.
A thrust bearing 110 is located between the housing 101 and the lug plate 104. The thrust bearing 110 receives a compression load, which is applied to the lug plate 104 through the pistons 108, the shoes 109, the swash plate 105, and the hinge mechanism 106.
A displacement control valve 111, which is an electromagnetic valve, varies the pressure in the crank chamber 102 and the compressor displacement in accordance with external signals, which are determined by the cooling load and the On/Off state-of the air-conditioning switch.
When each piston 108 moves from the bottom dead center to the top dead center, that is, in the compression stroke, refrigerant gas is compressed. When each piston 108 moves from the top dead center to the bottom dead center, that is, in the suction stroke, refrigerant gas is drawn to the corresponding cylinder bore 107.
As shown in FIG. 10, the swash plate 105 includes a location D1 corresponding to the top dead center position of the pistons 108 and a location D2 corresponding to the bottom dead center position of the pistons 108. The pistons 108 are in the compression stroke when coupled to the part from the top dead center location D1 to the bottom dead center location D2 in the rotation direction of the swash plate 105 (or drive shaft 103). That is, the pistons 108 that are coupled to the right side of the swash plate 105 from the imaginary plane H in FIG. 10 are in the compression stroke. The pistons 108 are in the suction stroke when coupled to the part from the bottom dead center location D2 to the top dead center location D1 in the rotation direction of the drive shaft 103. That is, the pistons 108 that are coupled to the left side of the swash plate 105 from the imaginary plane H in FIG. 10 are in the suction stroke. The imaginary plane H includes the top dead center location D1, the bottom dead center location D2, and the axis L.
Therefore, a pressing force directed toward the lug plate 104 is applied from the pistons 108 to the compression stroke side of the swash plate 105. On the other hand, a tractive force directed toward the cylinder bores 107 is applied from the pistons 108 to the suction stroke side of the swash plate 105. The tractive force is caused by the negative pressure in the cylinder bores 107.
Therefore, the force applied to one side of the swash plate 105 relative to the plane H is opposite to that applied to the other side. Accordingly, an inclination moment is applied to the piston-driving parts, which include the swash plate 105, the hinge mechanism 106, and the lug plate 104. This may incline the piston-driving parts relative to the housing 101 and may form a space between the lug plate 104 and the thrust bearing 110 and between the thrust bearing 110 and the housing 101. As a result, the rotation of the lug plate 104 may become unstable from chattering of the thrust bearing 110, and the lug plate 104 drives the thrust bearing 110 against the housing 101. This causes noise and vibration.
The illustrated compressor has a variable displacement. When the displacement is decreased, the control valve 111 increases the pressure in the crank chamber 102. As the pressure in the crank chamber 102 increases, the difference between the pressure in the crank chamber 102 applied to the front of the pistons 108 coupled to the compression stroke side and that in the cylinder bores 107 applied to the rear of the same pistons 108 decreases. At this time, the difference between the pressure in the crank chamber 102 applied to the front of the pistons 108 coupled to the suction stroke side and that in the cylinder bores 107 applied to the rear of the same pistons 108 increases. This increases the inclination moment applied to the piston-driving parts 104-106 and causes the previously mentioned problems.
There is a case in which the control valve 111, which is an electromagnetic valve controlled by the external signals, increases the pressure in the crank chamber 102 even if the cooling load is great. In other words, there is a case in which the displacement is decreased when the discharge pressure is high. In this case, the pressure in the crank chamber 102 increases to a very high level against the high pressure in the cylinder bores 107, which further increases the inclination moment applied to the piston-driving parts 104-106.
An objective of the present invention is to provide a piston-type compressor that reduces noise and vibration caused by the inclination of the piston-driving parts relative to the compressor housing.
To achieve the above objective, the present invention provides a piston-type compressor structured as follows. A housing includes a crank chamber and cylinder bores. Pistons are located in the corresponding cylinder bores. A drive shaft is supported by the housing and passes through the crank chamber. A piston-driving part is supported by the drive shaft in the crank chamber to rotate integrally with the drive shaft. The pistons are coupled to the piston-driving part. Gas in the cylinder bores is compressed when rotation of the drive shaft is converted into reciprocation of the pistons through the piston-driving part. A thrust bearing is located between the housing and the piston-driving part and receives a thrust load applied to the piston-driving part. The thrust bearing includes front and rear races and rolling elements located between the races. The front race is located between the rear race and the housing and the rear race is located between the front race and the piston-driving part. A front seat is formed on the housing for supporting the front race. A rear seat is formed on the piston-driving part for supporting the rear race. The diameters of the front and rear seats are different, which causes elastic deformation of the races when a thrust load is applied to the thrust bearing.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.